Aviation In Canada

Saturday, March 19, 2005

Intersections and Flight Planning

We're all familiar with the 5-letter fixes brought to us by ICAO. They're used for enroute navigation by RNAV equipped aircraft, as well as for approaches as step-down fixes, Intermediate Fixes (IF) and so on. There are some rules to them. Many are meant for RNAV-equipped aircraft, though some are compulsory reporting points at airway intersections and so on.

They are supposed to be pronounceable. There are several that are cute, some that are ambiguous, and some that just seem to defy that rule. For example, Nashville, Tennessee, has one called GITAR. Nicely appropriate. Then Orlando has SURFN. Not quite a gramatically correct spelling, but it works. People can figure out how to say it. Then there are those that have people guessing. For example, XOSUS. How does one pronounce the 'X' on the front? ICAO says it should pronounced as a 'Z' if it starts a name. Personally, I think it should be disallowed. If you want that pronounciation, use a 'Z'. The problem is that we are running out of them. So we use XOSUS and others like it, perhaps running a possibility of a problem. An unfamiliar pilot is cleared direct XOSUS and enters ZOSUS, which may also exist but be halfway around the world. Some are already close enough without having an 'X' involved. I once watched a pilot ask for clearance to a fix, receive it, and make a 90° left turn. He was cleared direct BIMKU, and apparently entered BIMTU in advertently. Inattention? Perhaps, but it happened nonetheless. It took us both by surprise. Also, there are several pronunciations which cause problems. PIKIL exists on the North Atlantic. If a pilot were cleared directly to PIKIL, and ATC said it like, "pickle,", should he enter PIKIL, PICKL, PIKEL, PICIL, or any other of a number of possible interpretations? First, the pilot should consider it in context. Is there a fix downstream on the flight plan route, or associated with an approach procedure at destination, or a fix on the SID plate on departure which might sound like the word spoken? Whatever the question, a quick request to ATC to spell it would reduce the chances of an incident like the one described above.

Lastly, there are other fixes which clearly are not pronounceable. These fixes are usually located in spots which are not necessary for navigation, but are marked on charts. The primary examples that come to mind are those on charts on the international (as opposed to FIR) boundaries. These fixes are marked on Canadian charts, but not named. Jeppesen charts have their names marked. These appear with "names" like BCVKH. They are not meant to be used in flight plans, and many Canadian controllers will not know what the heck you are talking about. I'm not sure how many US controllers would recognize them. Anyway, they are marked for reference only, hence the lack of naming on the Canadian charts, and the lack of a conventional, pronounceable name in general.